HORIZONTAL STRAIN FIELD AND TECTONIC DEFORMATION OF CHINA MAINLAND REVEALED BY PRELIMINARY GPS RESULT
JIANG ZAISEN 1 MA ZONGJIN 2 ZHANG XI 3 WANG QI 4 WANG SHUANGXU 3 1 Center for Analysis and Prediction, China Seismological Bureau, Beijing 100036,China 2 Institute of Geology, China Seismological Bureau, Beijing 100029, China 3 The Second Monitoring Center, China Seismological Bureau, Xian 710054,China 4 Institute of Seismology, China Seismological Bureau, Wuhan 430071, China
From the observations of various GPS networks during 1991～1999 and basic network of China Crustal Movement Observation Network during 1998～2000 in China Mainland, the united solution of horizontal velocities have been calculated in this paper. On the basis of assumption of continuous medium a model of horizontal velocity field is established with the aid of the least square collocation, and the preliminary results of horizontal strain fields (or called apparent strain fields) of China Mainland are presented. The characteristics of spatial distribution of horizontal motion and strain field, and their relationship with strong earthquakes are analyzed. A brief analysis is given for tectonic deformation background of the M S 8.1 earthquake on the west of Kunlun-mountain pass on Nov.14, 2001. The results show that strong tectonic deformation and high strain rate exist in the mid-western China Mainland, being the most remarkable in Qinghai-xizang block and its margins and western Xinjiang. In most of areas, except Sichuan-Yunnan and western Xinjiang, the nearly east-westward faults show sinistral shear deformation, while the nearly south-northward faults show dextral shear deformation. However the eastern China Mainland shows weaker tectonic deformation. Strong earthquakes occurred in the high-value region and its margins of shear strain rate, especially in the high-value region of shear strain rate in accordance with tectonic deformation background. The M S 8.1 earthquake on the west of Kunlun-mountain pass occurred in the most obvious high-value region of east-westward sinistral shear strain rate,and this region had tectonic deformation background that nearly east-westward fault produced dislocation of huge strike-slip rupture from the situation of strain.